1. Field of the Invention
The present invention relates to a lens driving device employed in an optical apparatus, more particularly, which, during frictional driving, generates a friction force necessary for driving a lens, with predetermined hardness maintained, but suffers minimal abrasion, thereby achieving stable operation properties and higher driving properties.
2. Description of the Related Art
In general, an optical apparatus includes a lens driving device for driving a lens using a cam structure, a screw or a piezoelectric element. The lens driving device employs a motor or the piezoelectric element to generate a driving force and the cam structure or the screw to transmit the driving force.
Therefore, the lens driving device drives the lens to change a relative distance of the lens, thereby performing zooming or focusing.
Meanwhile, the lens driving device utilized in a mega-pixel mobile phone chiefly adopts as a driving force a stepper motor, a voice coil motor (VCM), and a piezoelectric ultrasonic motor. The piezoelectric ultrasonic motor changes simple vibration such as shrinkage and expansion caused upon application of power to a piezoelectric body into circular or linear vibration due to friction between stators or rotors.
Thus the piezoelectric ultrasonic motor exhibits higher energy density, a quicker response rate and a higher location precision than an electromagnetic motor, also noise-free and not susceptible to electromagnetic waves.
U.S Patent Publication No. 2005-29876 and U.S Patent Publication No. 2005-62346 disclose a lens driving device including a vibrator composed of a body having piezoelectric sheets stacked therein, a guide shaft in contact with a driving contacting part disposed on top and bottom of the body, and a compressor generating a compression force between the driving contacting part and the guide shaft. In this lens driving device, the body is moved back and forth using ultrasonic vibration occurring in response to power applied to the body.
Accordingly, when two alternating current signals with a 90 degree phase difference are applied to the body of the vibrator, the body vibrates in both length and bending directions. Then a friction force between the driving contacting part and the guide shaft in contact with each other by the compressor is generated to move back and forth the body along the guide shaft.
Also, the driving contacting part in contact with the guide shaft is formed of a resin having abrasive particles such as alumina powder dispersed and solidified therein to achieve hardness and flexibility.
However, when the vibrator runs for long time, the friction force between the guide shaft and the driving contacting part causes the driving contacting part having a very rough surface to be abraded even though the driving contacting part is formed of a high-hardness material such as alumina ceramics AlO2 or silicon carbide SiC. Accordingly, foreign dusts from abrasion may infiltrate into sensitive parts to degrade characteristics of the device.